The 31648 is a clamp with 1 in. NPT threads that allows Campbell Scientific CS45X- and CRS45X-series submersible pressure transducers to be mated with a 1 in. PVC pipe for installations purposes. The 31648 Heyco fitting is not meant to be water tight, as water will likely fill the submerged pipe behind the fitting. However, the fitting does provide some protection to the sensor and cable from disturbances and debris. A 1 in. female adapter socket with FPT threads is needed between the 31648 and 1 in. PVC pipe. This adapter socket is typically available at stores that sell PVC pipe.
Note: In the image, the 31648 is shown attached to a pressure transducer.